Download Practice advisory for perioperative visual loss associated with spine

Practice Advisory for Perioperative Visual Loss
Associated with Spine Surgery
An Updated Report by the American Society of
Anesthesiologists Task Force on Perioperative Visual Loss
P
RACTICE Advisories are systematically developed reports that are intended to assist decision-making in areas of patient care. Advisories provide a synthesis and analysis
of expert opinion, clinical feasibility data, open forum commentary, and consensus surveys. Practice Advisories developed by the American Society of Anesthesiologists (ASA) are
not intended as standards, guidelines, or absolute requirements, and their use cannot guarantee any specific outcome.
They may be adopted, modified, or rejected according to
clinical needs and constraints and are not intended to replace
local institutional policies.
Practice Advisories are not supported by scientific literature to the same degree as standards or guidelines because of
the lack of sufficient numbers of adequately controlled studies. Practice Advisories are subject to periodic update or re-
• What other guideline statements are available on this topic?
X This Practice Advisory updates the “Practice Advisory for
Perioperative Visual Loss Associated with Spine Surgery,”
adopted by the ASA in 2005 and published in 2006.*
• Why was this Advisory developed?
X In October 2010, the Committee on Standards and Practice
Parameters elected to collect new evidence to determine
whether recommendations in the existing Practice Advisory
were supported by current evidence.
• How does this Advisory differ from existing guidelines?
X New evidence presented includes an updated evaluation of
scientific literature. The new findings did not necessitate a
change in recommendations.
• Why does this Advisory differ from existing guidelines?
X The ASA advisory differs from the existing guidelines because it provides new evidence obtained from recent scientific literature.
Updated by the Committee on Standards and Practice Parameters, Jeffrey L. Apfelbaum, M.D. (Committee Chair), Chicago, Illinois; Steven Roth, M.D. (Task Force Chair), Chicago, Illinois; Richard T. Connis, Ph.D., Woodinville, Washington; Karen B. Domino,
M.D., Seattle, Washington; Lorri A. Lee, M.D., Seattle, Washington;
David G. Nickinovich, Ph.D., Bellevue, Washington; and Mark A.
Warner, M.D., Rochester, Minnesota. The original document was
developed by the American Society of Anesthesiologists Task Force
on Perioperative Visual Loss: Mark A. Warner, M.D. (Chair), Rochester, Minnesota; James F. Arens, M.D., Houston, Texas; Richard T.
Connis, Ph.D., Woodinville, Washington; Karen B. Domino, M.D.,
Seattle, Washington; Lorri A. Lee, M.D., Seattle, Washington; Neil
Miller, M.D., Baltimore, Maryland; Sohail Mirza, M.D., Seattle, Washington; Nancy Newman, M.D., Atlanta, Georgia; David G. Nickinovich, Ph.D., Bellevue, Washington; Steven Roth, M.D., Chicago, Illinois; Peter Savino, M.D., Philadelphia, Pennsylvania; and Philip
Weinstein, M.D., San Francisco, California.
Received from the American Society of Anesthesiologists, Park
Ridge, Illinois. Submitted for publication October 20, 2011. Accepted for publication October 20, 2011. Supported by the American Society of Anesthesiologists and developed under the direction
of the Committee on Standards and Practice Parameters, Jeffrey L.
Apfelbaum, M.D. (Chair). Approved by the ASA House of Delegates on
October 19, 2011. The original Advisory was endorsed by the North
American Neuro-Ophthalmology Society and supported by the North
American Spine Society. A complete bibliography used to develop this
updated Advisory, arranged alphabetically by author, is available as
Supplemental Digital Content 1, http://links.lww.com/ALN/A785.
Address correspondence to the American Society of Anesthesiologists: 520 North Northwest Highway, Park Ridge, Illinois 600682573. This Practice Advisory, as well as all published ASA Practice
Parameters, may be obtained at no cost through the Journal Web
site, www.anesthesiology.org.
* American Society of Anesthesiologists Task Force on Perioperative Visual Loss: Practice Advisory for Perioperative Visual Loss
Associated with Spine Surgery: A Report by the American Society of
Anesthesiologists Task Force on Perioperative Blindness. ANESTHESIOLOGY
2006; 104:1319 –28.
vision as warranted by the evolution of medical knowledge,
technology, and practice.
This document updates the “Practice Advisory for Perioperative Visual Loss Associated with Spine Surgery: A Report by the American Society of Anesthesiologists Task Force
on Perioperative Blindness,” adopted by the ASA in 2005
and published in 2006.*
Methodology
A. Definition of Perioperative Visual loss
Visual loss after spine surgery is an uncommon occurrence.1–3 Ophthalmic complications have been reported
to occur in less than 0.2% of spine surgeries.4 – 8 For this
Advisory, perioperative visual loss refers to permanent impairment or total loss of sight associated with a spine
procedure during which general anesthesia is administered. The perioperative period includes the time period
from the immediate preoperative assessment through discharge from the acute healthcare facility. Conditions addressed in this Advisory include posterior ischemic optic
neuropathy (ION), anterior ION, and central retinal artery occlusion (CRAO). “High-risk patients” are defined
as those who undergo spine procedures while positioned
Supplemental digital content is available for this article. Direct
URL citations appear in the printed text and are available in
both the HTML and PDF versions of this article. Links to the
digital files are provided in the HTML text of this article on the
Journal’s Web site (www.anesthesiology.org).
Copyright © 2012, the American Society of Anesthesiologists, Inc. Lippincott
Williams & Wilkins. Anesthesiology 2012; 116:274 – 85
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prone and who have prolonged procedures, experience
substantial blood loss, or both.
loss were evaluated. Third, consultants who had expertise or
interest in perioperative visual loss and who practiced or
worked in various settings (e.g., academic and private practice) were asked to: (1) participate in opinion surveys on the
effectiveness of various perioperative management strategies,
and (2) review and comment on a draft of the Advisory
developed by the Task Force. Fourth, additional opinions
were solicited from active members of the Society for Neuroscience in Anesthesiology and Critical Care (SNACC),
NANOS, and the North American Spine Society (NASS).
Fifth, the Task Force held an open forum at a national anesthesia meeting to solicit input on the key concepts of this
Advisory.† Sixth, all available information was used to build
consensus within the Task Force on the Advisory. A summary of recommendations may be found in appendix 1.
The draft document was made available for review on the
ASA website, and input was invited via e-mail announcement to all ASA members. All submitted comments were
considered by the Task Force in preparing the final draft.
In 2009, the ASA Committee on Standards and Practice
Parameters requested that scientific evidence for this Advisory
be updated. The update consists of an evaluation of literature
published after completion of the original Advisory.
B. Purpose of the Advisory
The purpose of this Advisory is to enhance awareness and
reduce the frequency of perioperative visual loss.
C. Focus
This Advisory focuses on the perioperative management of
patients who are undergoing spine procedures while they are
positioned prone and receiving general anesthesia. This Advisory does not address the perioperative management of
patients who receive regional anesthesia or sedation. This
Advisory also does not include other causes of visual loss,
such as cortical blindness. It does not include nonspine surgical procedures (e.g., cardiac surgery, radical neck dissection). In addition, this Advisory does not apply to young
children because of the rarity of visual loss in children
younger than 12 years of age undergoing spine surgery.
D. Application
This Advisory is intended for use by anesthesiologists, spine
surgeons, and all other individuals who deliver or who are
responsible for anesthesia or perioperative care. These individuals may include orthopedic surgeons, neurosurgeons,
ophthalmologists, neuro-ophthalmologists, neurologists,
nurse anesthetists, perioperative nurses, and anesthesiology
assistants. The Advisory may also serve as a resource for other
physicians, nurses, and healthcare professionals who manage
anesthetized patients.
F. Availability and Strength of Evidence
Preparation of this update used the same methodological
process as was used in the original Advisory to obtain new
scientific evidence. Opinion-based evidence obtained from
the original Advisory is reported in this update. The protocol
for reporting each source of evidence is described below.
G. Scientific Evidence
Study findings from published scientific literature were aggregated and are reported in summary form by evidence category, as described below. All literature (e.g., randomized
controlled trials, observational studies, case reports) relevant
to each topic was considered when evaluating the findings.
However, for reporting purposes in this document, only the
highest level of evidence (i.e., level 1, 2, or 3 identified below)
within each category (i.e., A, B, or C) is included in the
summary.
Category A: Supportive Literature. Randomized controlled
trials report statistically significant (P ⬍ 0.01) differences between clinical interventions for a specified clinical outcome.
Level 1: The literature contains multiple randomized controlled trials, and the aggregated findings are supported by
meta-analysis.‡
Level 2: The literature contains multiple randomized controlled trials, but there is an insufficient number of studies to
conduct a viable meta-analysis.
Level 3: The literature contains a single randomized controlled trial.
Category B: Suggestive Literature. Information from observational studies permits inference of beneficial or harmful relationships among clinical interventions and clinical outcomes.
E. Task Force Members and Consultants
The original Advisory was developed by an ASA-appointed
task force of 10 members, consisting of four anesthesiologists
from various geographic areas of the United States, three
neuro-ophthalmologists (one neurologist, two ophthalmologists), an orthopedic spine surgeon, a neurosurgeon, and
two methodologists from the ASA Committee on Standards
and Practice Parameters. Three physicians served as official
liaisons from national organizations. They included a neuroophthalmologist (North American Neuro-Ophthalmology
Society [NANOS]), an orthopedic surgeon (American Academy of Orthopaedic Surgeons), and a neurosurgeon (American Association of Neurological Surgeons).
The Task Force developed the original Advisory by means
of a six-step process. First, it reached consensus on the criteria
for evidence of effective perioperative interventions for the
prevention of visual loss. Second, original published articles
from peer-reviewed journals relevant to perioperative visual
† Society for Ambulatory Anesthesia, 20th Annual Meeting, May
13, 2005, Scottsdale, Arizona.
‡ Practice Advisories lack the support of a sufficient number of adequately controlled studies required to conduct an appropriate meta-analysis. Therefore, Categories A1 and C1 evidence are not reported in this
document.
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Level 1: The literature contains observational comparisons (e.g., cohort, case-control research designs) of clinical
interventions or conditions and indicates statistically significant differences between clinical interventions for a specified
clinical outcome.
Level 2: The literature contains noncomparative observational studies with associative (e.g., relative risk, correlation)
or descriptive statistics.
Level 3: The literature contains case reports.
Category C: Equivocal Literature. The literature cannot
determine whether there are beneficial or harmful relationships among clinical interventions and clinical outcomes.
Level 1: Meta-analysis did not find significant differences
among groups or conditions.
Level 2: The number of studies is insufficient to conduct
meta-analysis, and (1) randomized controlled trials have not
found significant differences among groups or conditions or
(2) randomized controlled trials report inconsistent findings.
Level 3: Observational studies report inconsistent findings
or do not permit inference of beneficial or harmful relationships.
Category D: Insufficient Evidence from Literature. The lack
of scientific evidence in the literature is described by the following terms.
Inadequate: The available literature cannot be used to assess
relationships among clinical interventions and clinical outcomes. The literature either does not meet the criteria for content as defined in the “Focus” of the Advisory or does not permit
a clear interpretation of findings due to methodological concerns (e.g., confounding in study design or implementation).
Silent: No identified studies address the specified relationships among interventions and outcomes.
a modal response of “agree” will be listed in the text as an
agreement).
Advisories
I. Preoperative Patient Evaluation and Preparation
There are no clinical trials addressing the impact of performing a focused preoperative evaluation for perioperative visual
loss.§ However, two observational studies report that preoperative anemia, vascular risk factors (e.g., hypertension, diabetes, peripheral vascular disease, coronary artery disease),
obesity, and tobacco use may be associated with perioperative visual loss (Category B2 evidence).5,9
Case reports suggest that perioperative visual loss may
occur after prolonged procedures10 –17 or substantial intraoperative blood loss18 –25 (Category B3 evidence). In addition,
observational studies report visual loss among patients undergoing prolonged procedures during which substantial
blood loss occurred (Category B2 evidence).5,26,27
The consultants and specialty society members disagree
that an ophthalmic or neuro-ophthalmic evaluation is effective in identifying patients at risk for perioperative visual loss.
The consultants and specialty society members agree that
vascular risk factors increase the risk of perioperative visual
loss. In addition, they agree that (1) the preoperative presence of anemia, (2) prolonged procedures, (3) substantial
blood loss, and (4) prolonged procedures combined with
substantial blood loss all increase the risk of perioperative
visual loss. The consultants and specialty society members
consider procedures to be prolonged when they exceed an
average of 6.5 h (range, 2–12 h) duration. They consider
blood loss to be substantial when the loss reaches an average
of 44.7% (range, 10 –200%) of estimated blood volume.
Advisory for Preoperative Patient Evaluation and Preparation. Although the consultants and specialty society members agree that there are identifiable preoperative risk factors,
at this time the Task Force does not believe that there are
identifiable preoperative patient characteristics that predispose patients to perioperative ION. In addition, the Task
Force believes that there is no evidence that an ophthalmic or
neuro-ophthalmic evaluation would be useful in identifying
patients at risk for perioperative visual loss. The Task Force
believes that the risk of perioperative ION may be increased
in patients who undergo prolonged procedures, have substantial blood loss, or both.储 Consider informing patients in
whom prolonged procedures, substantial blood loss, or both
are anticipated that there is a small, unpredictable risk of
perioperative visual loss. Because the frequency of visual loss
after spine surgery of short duration is very low, the decision
to inform patients who are not anticipated to be “high risk”
for visual loss should be determined on a case-by-case basis.
H. Opinion-based Evidence
The original Advisory contained formal survey information
collected from expert consultants and samples of active
members of the SNACC, NANOS, and the NASS. Additional information was obtained from open forum presentations and other invited and public sources. All opinion-based
evidence relevant to each topic (e.g., survey data, open-forum
testimony, Internet-based comments, letters, editorials) was
considered in the development of the original Advisory.
However, only the findings obtained from formal surveys are
reported.
Survey responses from Task Force-appointed expert consultants and specialty society members obtained during development of the original Advisory are summarized in the
text and reported in appendix 2, tables 1– 4.
Responses were solicited from four response categories:
agree, equivocal, disagree, and no opinion. Survey information is summarized in the text based on modal responses (e.g.,
§ Refer to appendix 2 for details of the literature review and data
analyses.
储 For the purposes of this Advisory, the Task Force considers such
patients (hereafter referred to as “high-risk patients”) to have a higher
risk for perioperative visual loss than patients who do not undergo
prolonged procedures, have substantial blood loss, or both.
Anesthesiology 2012; 116:274 – 85
II. Intraoperative Management
Intraoperative management consists of (1) blood pressure
management, (2) management of intraoperative fluids, (3)
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NANOS and NASS members report no opinion. The Consultants, SNACC members, and NASS members agree that
central venous pressure monitoring should be used in highrisk patients; the NANOS members report no opinion.
Advisory for Management of Intraoperative Fluids. Central
venous pressure monitoring should be considered in highrisk patients. Colloids should be used along with crystalloids
to maintain intravascular volume in patients who have substantial blood loss.
Management of Anemia. The literature is insufficient to
evaluate the efficacy of intraoperative management of anemia
during spine surgery (Category D evidence). One retrospective
comparison of patients who experienced perioperative visual
loss after spine surgery with a matched control group found
no difference in lowest recorded hematocrit values between
groups27 (Category B2 evidence).
The consultants and specialty society members agree that
hemoglobin or hematocrit values should be monitored periodically to detect anemia in high-risk patients. Those who
agree indicate that intraoperative hemoglobin or hematocrit
should be maintained at a minimum average of 9.4 g/dl
(range, 6 –13 g/dl) or 28% (range, 18 –37%), respectively.
Advisory for Management of Anemia. Hemoglobin or hematocrit values should be monitored periodically during surgery in high-risk patients who experience substantial blood
loss. The Task Force believes that there is no documented
lower limit of hemoglobin concentration that has been associated with the development of perioperative visual loss.
Therefore, the Task Force believes a transfusion threshold
that would eliminate the risk of perioperative visual loss related to anemia cannot be established at this time.
Use of Vasopressors. The literature is insufficient to evaluate the prolonged use of high-dose ␣-adrenergic agonists
during spine surgery (Category D evidence). The SNACC
members agree that prolonged use of high-dose ␣-adrenergic
agonists may reduce perfusion of the optic nerve in high-risk
patients; the consultants are equivocal, and the NANOS and
NASS members report no opinion.
Advisory for Use of Vasopressors. The Task Force consensus is that there is insufficient evidence to provide guidance
for the use of ␣-adrenergic agonists in high-risk patients during spine surgery. Therefore, the decision to use ␣-adrenergic
agonists should be made on a case-by-case basis.
Patient Positioning. Case reports suggest that patient positioning resulting in direct pressure to eyes (e.g., from the use
of a headrest, sheet roll, or other device) may precede the
onset of CRAO or retinal ischemia in spine surgery patients
(Category B3 evidence).#13–16,25,33– 42 One observational
study indicates that, in 19% of ION cases listed in the ASA
Visual Loss Registry, patient head position was maintained
with Mayfield pins with the eyes free of pressure9 (Category
B2 evidence).
The consultants and specialty society members agree that
direct pressure on the eye should be avoided to reduce the
risk of CRAO and other ocular damage. The consultants and
management of anemia, (4) use of vasopressors, (5) patient
positioning, and (6) staging of surgical procedures.
Blood Pressure Management. Blood pressure management
of high-risk patients depends on multiple patient characteristics,
such as the preoperative presence of chronic hypertension, cardiac dysfunction, and renal and vascular disease. In addition,
there are many intraoperative factors, such as fluid management, rate of blood loss, hypotension, and administration of
vasopressors, that affect blood pressure management. Case reports indicate perioperative visual loss occurring after procedures in which intraoperative hypotension was maintained for
patients without hypertension10,19,20,28 –30 or for patients with
well-controlled chronic hypertension30,31 (Category B3 evidence).
The Consultants and specialty society members disagree
with the survey statement “Deliberate hypotension techniques may be used in high-risk patients” (i.e., for high-risk
patients without preoperative chronic hypertension or for
high-risk patients with well-controlled preoperative chronic
hypertension). However, NASS members are split equally in
their opinions between agree and disagree for patients without preoperative chronic hypertension. Consultants and specialty society members who agree that deliberate hypotension may be used in patients without preoperative chronic
hypertension indicate that blood pressure should be maintained on average within 24% (range, 0 – 40%) of estimated
baseline mean arterial pressure or with a minimum systolic
blood pressure of 84 mmHg (range, 50 –120 mmHg).
Advisory for Blood Pressure Management. Systemic blood
pressure should be monitored continually in high-risk patients. The Task Force believes that the use of deliberate hypotensive techniques during spine surgery has not been shown
to be associated with the development of perioperative visual
loss. Therefore, the use of deliberate hypotension for these patients should be determined on a case-by-case basis.
Management of Intraoperative Fluids. The literature is insufficient to assess the relationship between the monitoring
of intravascular volume and the occurrence of visual loss among
spine surgery patients (Category D evidence). Although the use of
large volumes of crystalloids may be associated with increased
intraoperative ocular pressure, periorbital edema, and doublevision in patients undergoing cardiopulmonary bypass,32 the
literature is insufficient to address these issues in spine surgery
patients (Category D evidence).
The consultants, SNACC, NANOS, and NASS members
agree that intravascular volume should be monitored continually in high-risk patients. The consultants, SNACC members, and NANOS members agree that the balance between
colloid and crystalloid fluid resuscitation and replacement
has an impact on the potential for perioperative vision loss;
the NASS members report no opinion. The Consultants and
SNACC members are equivocal regarding the preference of
colloids over crystalloids for fluid resuscitation and replacement to reduce the potential for perioperative vision loss; the
# Although observational literature on the pathophysiology of retinal
vascular occlusion in humans is lacking, animal studies are available.
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SNACC members agree that the patient’s head should be
positioned level with or higher than the heart in high-risk
patients; NANOS member opinion is split equally between
agree and equivocal, and NASS member opinion is split
equally among agree, equivocal, and no opinion. The consultants, SNACC members, and NASS members agree that
the patient’s head should be placed in a neutral forward position in high-risk patients; the NANOS members report no
opinion. The consultants, SNACC, and NANOS members
agree that the type of head positioning device is not associated with perioperative ION; the NASS members disagree.
The consultants and all specialty society members agree that
the use of a horseshoe headrest may increase the risk of ocular
compression and perioperative CRAO. They all agree that
the eyes of prone-positioned patients should be assessed regularly and documented. In addition, they all agree that perioperative facial edema is common in high-risk patients.
Advisory for Patient Positioning. The Task Force believes
that there is no pathophysiologic mechanism by which facial
edema can cause perioperative ION. There is no evidence
that ocular compression causes isolated perioperative anterior ION or posterior ION. However, direct pressure on the
eye should be avoided to prevent CRAO. The high-risk patient should be positioned so that the head is level with or
higher than the heart when possible. The high-risk patient’s
head should be maintained in a neutral forward position
(e.g., without significant neck flexion, extension, lateral flexion, or rotation) when possible.
Staging of Surgical Procedures. The majority of spine surgery patients who experience perioperative ION undergo prolonged procedures with substantial blood loss while they are
positioned prone. Although the literature is insufficient to examine the impact of surgical staging on reducing the frequency
of perioperative visual loss in spine surgery patients (Category D
evidence), an observational study indicates that, in 94% of ION
cases listed in the ASA Visual Loss Registry, anesthetic duration
exceeded 6 h9 (Category B2 evidence). A related retrospective
study reported an association between duration of anesthesia
and frequency of eye injury after a mix of nonocular surgeries43
(Category B2 evidence).
The consultants and specialty society members agree
that consideration should be given to staging procedures
that are anticipated to be lengthy. Members of the specialty societies agree with the staging of procedures that
are anticipated to have substantial blood loss; consultant
opinion is split equally between agree and equivocal. All
groups agree with the staging of procedures that are anticipated to be lengthy and have substantial blood loss. The
consultants and specialty society members consider procedures to be prolonged when they exceed an average 6.5 h
(range, 2–12 h) in duration. They consider blood loss to
be substantial when the loss reaches an average of 44.7%
(range, 10 –200%) of estimated blood volume.
Advisory for Staging of Surgical Procedures. Although the
use of staged spine surgery procedures in high-risk paAnesthesiology 2012; 116:274 – 85
tients may entail additional costs and patient risks (e.g.,
infection, thromboembolism, or neurologic injury), it
also may decrease these risks and the risk of perioperative
visual loss in some patients. Therefore, consideration
should be given to the use of staged spine procedures in
high-risk patients.
IV. Postoperative Management
The literature is insufficient to evaluate the use of magnetic
resonance imaging to assess the extent of visual loss after
spine surgery in patients with posterior ION (Category D
evidence). A case report of a spine surgery patient with bilateral POIN indicated that visual recovery occurred after the deliberate maintenance of increased hematocrit and blood pressure (Category B3 evidence).8 One case report found no visual
improvement after a 1-week course of high-dose steroids to treat
a patient with ION subsequent to lumbar spinal fusion (Category C3 evidence).30 The literature is insufficient to evaluate the
use of antiplatelet agents or intraocular pressure-lowering agents
in the treatment of ION (Category D evidence).
The consultants and specialty society members agree that
magnetic resonance imaging may be useful to detect causes of
visual loss other than ION and CRAO (e.g., cortical blindness, pituitary apoplexy). All groups agree that a high-risk
patient’s vision should be assessed when the patient becomes
alert. The consultants and specialty society members agree
that, in high-risk patients for whom ION is suspected, hemoglobin or hematocrit values should be adjusted upward,
blood pressure should be increased, and oxygen should be
administered.
The consultants and SNACC members are equivocal,
NANOS member opinion is split equally between agree and
equivocal, and NASS members report no opinion regarding
the statement that there is no role for steroids, antiplatelet
agents, or intraocular pressure-lowering agents in the treatment of perioperative ION. All groups agree that there is no
proven treatment for perioperative ION.
Advisory for Postoperative Management. The consensus of
the Task Force is that a high-risk patient’s vision should be
assessed when the patient becomes alert (e.g., in the recovery
room, intensive care unit, or nursing floor). If there is concern
regarding potential visual loss, an urgent ophthalmologic consultation should be obtained to determine its cause. Additional
management may include optimizing hemoglobin or hematocrit values, hemodynamic status, and arterial oxygenation. To
rule out intracranial causes of visual loss, consider magnetic resonance imaging. The Task Force believes that there is no role for
antiplatelet agents, steroids, or intraocular pressure-lowering
agents in the treatment of perioperative ION.
Appendix 1: Summary of Advisory
Statements
I. Preoperative Patient Evaluation and Preparation
• Although the consultants and specialty society members agree
that there are identifiable preoperative risk factors, at this time the
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•
•
•
•
• The high-risk patient should be positioned so that the head is
level with or higher than the heart when possible.
• The high-risk patient’s head should be maintained in a neutral
forward position (e.g., without significant neck flexion, extension, lateral flexion, or rotation) when possible.
Task Force does not believe that there are identifiable preoperative
patient characteristics that predispose patients to perioperative ION.
Further, the Task Force believes that there is no evidence that an
ophthalmic or neuro-ophthalmic evaluation would be useful in
identifying patients at risk for perioperative visual loss.
The Task Force believes that the risk of perioperative ION may
be increased in patients who undergo prolonged procedures, have
substantial blood loss, or both.**
Consider informing patients in whom prolonged procedures,
substantial blood loss, or both are anticipated that there is a small,
unpredictable risk of perioperative visual loss.
Because the frequency of visual loss after spine surgery of short
duration is very low, the decision to inform patients who are not
anticipated to be “high risk” for visual loss should be determined
on a case-by-case basis.
III. Staging of Surgical Procedures
• Although the use of staged spine surgery procedures in high-risk
patients may entail additional costs and patient risks (e.g., infection, thromboembolism, or neurologic injury), it also may decrease these risks and the risk of perioperative visual loss in some
patients.
䡩 Therefore, consideration should be given to the use of staged
spine procedures in high-risk patients.
IV. Postoperative Management
II. Intraoperative Management
• The consensus of the Task Force is that a high-risk patient’s
vision should be assessed when the patient becomes alert (e.g., in
the recovery room, intensive care unit, or nursing floor).
• If there is concern regarding potential visual loss, an urgent ophthalmologic consultation should be obtained to determine its
cause.
• Additional management may include optimizing hemoglobin or hematocrit values, hemodynamic status, and arterial oxygenation.
• To rule out intracranial causes of visual loss, consider magnetic
resonance imaging.
• The Task Force believes that there is no role for antiplatelet
agents, steroids, or intraocular pressure-lowering agents in the
treatment of perioperative ION.
Blood Pressure Management
• Systemic blood pressure should be monitored continually in
high-risk patients.
• The Task Force believes that the use of deliberate hypotensive
techniques during spine surgery has not been shown to be
associated with the development of perioperative visual loss.
䡩 Therefore, the use of deliberate hypotension for these patients should be determined on a case-by-case basis.
Management of Intraoperative Fluids
• Central venous pressure monitoring should be considered in
high-risk patients.
• Colloids should be used along with crystalloids to maintain intravascular volume in patients who have substantial blood loss.
Management of Anemia
• Hemoglobin or hematocrit values should be monitored periodically during surgery in high-risk patients who experience substantial blood loss.
• The Task Force believes that there is no documented lower limit
of hemoglobin concentration that has been associated with the
development of perioperative visual loss.
䡩 Therefore, the Task Force believes a transfusion threshold that
would eliminate the risk of perioperative visual loss related to
anemia cannot be established at this time.
Use of Vasopressors
• The Task Force consensus is that there is insufficient evidence to
provide guidance for the use of ␣-adrenergic agonists in high-risk
patients during spine surgery.
䡩 Therefore, the decision to use ␣-adrenergic agonists should be
made on a case-by-case basis.
Patient Positioning
• The Task Force believes that there is no pathophysiologic mechanism by which facial edema can cause perioperative ION.
• There is no evidence that ocular compression causes isolated perioperative anterior ION or posterior ION.
䡩 However, direct pressure on the eye should be avoided to
prevent CRAO.
Appendix 2: Methods and Analyses
A. State of the Literature
For this updated Advisory, a review of studies used in the development of the original Advisory was combined with a review of studies
published subsequent to approval of the original Advisory. The
updated literature review was based on evidence linkages, consisting
of directional statements about relationships between specific perioperative management activities associated with a spine procedure
during which general anesthesia is administered and permanent
impairment or total loss of sight. The evidence linkage interventions are listed below.††
Preoperative Patient Evaluation and Preparation
Ophthalmic or neuro-ophthalmic evaluation
Vascular risk factors
Preoperative anemia
Prolonged procedures
Substantial blood loss
Prolonged procedures combined with substantial blood loss
Intraoperative Management
Blood Pressure Management
Deliberate hypotension techniques in high-risk patients without preoperative chronic hypertension
Deliberate hypotension techniques in high-risk patients with
well-controlled preoperative chronic hypertension
Management of Intraoperative Fluids
Continual intravascular volume monitoring for high-risk patients
Central venous pressure monitoring for high-risk patients
** For the purposes of this Advisory, the Task Force considers
such patients to have a higher risk for perioperative visual loss than
patients who do not undergo prolonged procedures, have substantial blood loss, or both.
†† Unless otherwise specified, outcomes for the listed interventions refer to the occurrence of perioperative visual loss.
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eliminates reports that contain only opinion; (3) the study must
report a clinical finding or set of findings that can be identified
as the product of an original investigation or report. This criterion eliminates the repetitive reporting and counting of the same
results, as may occur in review articles or follow-up studies that
summarize previous findings, and (4) the study must use sound
research methods and analytical approaches that provide a clear
test or indication of the relationship between the intervention
and outcome of interest. Because none of the studies in this
updated Advisory met all four criteria, the published literature
could not be used as a source of quantitative support.
Although evidence linkages are designed to assess causality, the
reviewed studies did not provide a clear indication of causality. Therefore, the published literature could not be used as a source of quantitative support. However, many published studies were evaluated that
provided the Task Force with important noncausal evidence. For example, descriptive literature (i.e., reports of frequency or incidence) is
often useful in providing an indication of the scope of a problem, and
case reports may be useful in identifying perioperative events that may
be precursors to permanent visual impairment or total loss of sight. In
conclusion, the current literature has not been helpful in determining
the efficacy of specific perioperative management activities (i.e., associated with a spine procedure during which general anesthesia is administered) in reducing permanent impairment or total loss of sight. Until
controlled studies are conducted, evidence from noncausal sources will
need to be used, such as consensus-driven data and the opinion of
practitioners and experts. It is recommended that future research on
perioperative visual loss focus on the identification of patients at higher
risk of perioperative visual loss in the context of prospective research
designs when feasible.
In the original Advisory, interobserver agreement among Task
Force members and two methodologists was established by interrater reliability testing. Agreement levels using a kappa (␬) statistic for
two-rater agreement pairs were as follows: (1) type of study design,
␬ ⫽ 0.64 – 0.78; (2) type of analysis, ␬ ⫽ 0.74 – 0.87; (3) evidence
linkage assignment, ␬ ⫽ 0.69 – 0.94; and (4) literature inclusion for
database, ␬ ⫽ 0.77–1.00. Three-rater chance-corrected agreement
values were: (1) study design, Sav ⫽ 0.69, Var (Sav) ⫽ 0.022; (2)
type of analysis, Sav ⫽ 0.82, Var (Sav) ⫽ 0.017; (3) linkage assignment, Sav ⫽ 0.79, Var (Sav) ⫽ 0.007; and (4) literature database
inclusion, Sav ⫽ 0.86 Var (Sav) ⫽ 0.030. These values represent
moderate-to-high levels of agreement. For the updated Advisory,
the same two methodologists involved in the original Advisory conducted the literature review.
Colloid and crystalloid balance for fluid resuscitation
Colloids versus crystalloids for fluid resuscitation and replacement
Management of Anemia
Periodic monitoring of hemoglobin or hematocrit values
Vasopressors
Prolonged use of high-dose ␣-adrenergic agonists in high-risk patients
Patient Positioning
Avoidance of direct pressure on the eye
Positioning of head level with or higher than the heart in high-risk
patients
Placing head in a neutral forward position in high-risk patients
Type of head positioning device
Use of a horseshoe headrest
Regular assessment and documentation of the eyes of pronepositioned patients
Occurrence of perioperative facial edema in high-risk patients
Surgical Procedures
Staging of procedures anticipated to be lengthy
Staging of procedures anticipated to have substantial blood loss
Staging of procedures anticipated to be lengthy with substantial
blood loss
Postoperative Management
Assessing a high-risk patient’s vision when the patient becomes alert
Magnetic resonance imaging
Adjusting hemoglobin or hematocrit values upward in patients
for whom ION is suspected
Increasing blood pressure in patients for whom ION is suspected
Administering arterial oxygenation in patients for whom ION is
suspected
Administering antiplatelet agents, steroids, or intraocular pressure-lowering agents
For purposes of literature review, potentially relevant clinical
studies were identified via electronic and manual searches of the
literature. The updated electronic search covered a 10-yr period
from 2002 through 2011. The manual search covered a 15-yr
period of time from 1997 through 2011. More than 100 new
citations that addressed topics related to the evidence linkages
were identified. These articles were reviewed and combined
with pre-2006 articles used in the original Advisory, resulting
in a total of 51 articles that contained direct linkage-related
evidence.
No evidence linkage contained sufficient literature with welldefined experimental designs and statistical information to conduct an analysis of aggregated studies (i.e., meta-analysis). A
complete bibliography used to develop this updated Advisory,
organized by section, is available as Supplemental Digital Content 2, http://links.lww.com/ALN/A786.
A study or report that appears in the published literature can
be included as evidence in the development of an advisory if it
meets four essential criteria. Failure to meet one or more of these
criteria means that a study had features that did not make it
suitable for analytic purposes. The four essential criteria are as
follows: (1) the study must be related to one of the specified
linkage statements; (2) the study must report a clinical finding or
set of findings that can be tallied or quantified. This criterion
B. Consensus-based Evidence
For the original Advisory, consensus was obtained from multiple
sources, including (1) survey opinion from consultants who were
selected based on their knowledge or expertise regarding perioperative visual impairment or total loss of sight associated with a
spine procedure during which general anesthesia is administered; (2) survey opinions from selected samples of active members of the SNACC, NANOS, and NASS; (3) testimony from
attendees of a publicly held open forum at a national anesthesia
meeting,‡‡ (4) Internet commentary, and (5) Task Force opinion and interpretation. The consultant survey rate of return was
60% (N ⫽ 18 of 30). Modal survey responses for consultants
and specialty group members are presented in the text of the
Advisory, and complete listings of survey responses are reported
in tables 1– 4.
‡‡ Society for Ambulatory Anesthesia 20th Annual Meeting,
Scottsdale, Arizona, May 13, 2005.
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Table 1. Consultant Survey: Percentage Responses*
Evidence Linkage/Intervention†
1. Preoperative patient evaluation and preparation
Ophthalmic or neuro-ophthalmic evaluation
Vascular risk factors
Preoperative anemia
Prolonged procedures
Substantial blood loss
Prolonged procedures combined with substantial
blood loss
2. Intraoperative blood pressure management
Deliberate hypotension in high-risk patients without
preoperative chronic hypertension
Deliberate hypotension in high-risk patients with
well-controlled preoperative chronic hypertension
3. Management of intraoperative fluids
Intravascular volume should be monitored continually
in high-risk patients
Balance between colloid and crystalloid fluid
resuscitation and replacement
Colloids are preferred over crystalloids
CVP monitoring for high-risk patients
4. Management of anemia
Periodic monitoring of Hgb or Hct for high-risk patients
5. Vasopressors:
Prolonged use of high-dose
␣-adrenergic agonists in high-risk patients
6. Patient positioning
Avoid direct pressure on the eye
Head position level with or higher than the heart in
high-risk patients
Neutral forward position of head in high-risk patients
Head positioning device not associated with AION or
PION
Horseshoe headrest may increase ocular
compression and perioperative CRAO
Regular assessment and documentation of eyes of
prone-positioned patients
Perioperative facial edema is common in high-risk
patients
7. Surgical procedures
Staging of lengthy procedures
Staging of procedures with substantial blood loss
Staging of lengthy procedures with substantial blood
loss
8. Postoperative management
Assessment of a high-risk patient’s vision when the
patient becomes alert
No proven treatment for perioperative AION or PION
MRI to eliminate causes other than ION and CRAO
In high-risk patients for whom ION is suspected,
adjust Hgb or Hct values upward, increase blood
pressure, and administer arterial oxygenation
No role for antiplatelet agents, steroids, or intraocular
pressure-lowering agents in the treatment of
perioperative ION
Disagree
No
Opinion
N
Agree
Equivocal
18
18
18
18
18
18
16.7
77.8*
50.0*
100.0*
88.9*
94.4*
33.3
5.6
27.8
0.0
11.1
5.6
44.4*
5.6
16.9
0.0
0.0
0.0
5.6
11.1
5.6
0.0
0.0
0.0
18
22.2
33.3
44.4*
0.0
18
5.6
38.9
55.6*
0.0
17
64.7*
35.3
0.0
0.0
18
38.9*
27.8
27.8
5.6
18
18
22.2
38.9*
44.4*
33.3
27.8
22.2
5.6
5.6
17
18
100.0*
27.8
0.0
50.0*
0.0
5.6
0.0
16.7
18
18
100.0*
61.1*
0.0
22.2
0.0
5.6
0.0
11.1
17
18
47.1*
83.3*
41.2
16.7
5.9
0.0
5.9
0.0
18
83.3*
11.1
5.6
0.0
18
88.9*
5.6
5.6
0.0
17
76.5*
0.0
23.5
0.0
18
18
18
50.0*
44.4*
66.7*
44.4
44.4*
27.8
0.0
0.0
0.0
5.6
11.1
5.6
18
83.3*
16.7
0.0
0.0
18
18
17
77.8*
77.8*
76.5*
11.1
0.0
23.5
5.6
5.6
0.0
5.6
16.7
0.0
17
35.3
52.9*
5.9
5.9
* Modal response. † Refer to the text in the Advisory for the full wording of the questionnaire items.
AION ⫽ anterior ischemic optic neuropathy; CRAO ⫽ central retinal artery occlusion; CVP ⫽ central venous pressure; Hct ⫽ hematocrit;
Hgb ⫽ hemoglobin; ION ⫽ ischemic optic neuropathy; MRI ⫽ magnetic resonance imaging; N ⫽ number of consultants who responded
to each item; PION ⫽ posterior ischemic optic neuropathy.
Anesthesiology 2012; 116:274 – 85
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Table 2. Society for Neuroscience in Anesthesiology and Critical Care Member Survey: Percentage Responses*
Evidence Linkage/Intervention†
1. Preoperative patient evaluation and preparation
Ophthalmic or neuro-ophthalmic evaluation
Vascular risk factors
Preoperative anemia
Prolonged procedures
Substantial blood loss
Prolonged procedures combined with substantial
blood loss
2. Intraoperative blood pressure management
Deliberate hypotension in high-risk patients without
preoperative chronic hypertension
Deliberate hypotension in high-risk patients with
well-controlled preoperative chronic hypertension
3. Management of intraoperative fluids
Intravascular volume should be monitored continually
in high-risk patients
Balance between colloid and crystalloid fluid
resuscitation and replacement
Colloids are preferred over crystalloids
CVP monitoring for high-risk patients
4. Management of anemia
Periodic monitoring of Hgb or Hct for high-risk
patients
5. Vasopressors
Prolonged use of high-dose ␣-adrenergic agonists in
high-risk patients
6. Patient positioning
Avoid direct pressure on the eye
Head position level with or higher than the heart in
high-risk patients
Neutral forward position of head in high-risk patients
Head positioning device not associated with AION or
PION
Horseshoe headrest may increase ocular
compression and perioperative CRAO
Regular assessment and documentation of eyes of
prone-positioned patients
Perioperative facial edema is common in high-risk
patients
7. Surgical procedures
Staging of lengthy procedures
Staging of procedures with substantial blood loss
Staging of lengthy procedures with substantial blood
loss
8. Postoperative management
Assessment of a high-risk patient’s vision when the
patient becomes alert
No proven treatment for perioperative AION or PION
MRI to eliminate causes other than ION and CRAO
In high-risk patients for whom ION is suspected,
adjust Hgb or Hct values upward, increase blood
pressure, and administer arterial oxygenation
No role for antiplatelet agents, steroids, or intraocular
pressure-lowering agents in the treatment of
perioperative ION
N
Agree
Equivocal
Disagree
Opinion
126
127
127
127
126
126
16.7
74.8*
55.9*
85.0*
84.1*
90.5*
27.8
16.5
26.0
9.4
9.5
6.3
39.7*
3.1
13.4
2.4
4.8
1.6
15.9
5.5
4.7
3.1
1.6
1.6
127
19.7
16.5
59.8*
3.9
127
17.3
16.5
63.0*
3.1
127
66.9*
22.0
9.4
1.6
127
29.9*
29.1
28.3
12.6
127
127
22.0
41.7*
35.4*
33.1
34.6
23.6
7.9
1.6
127
93.7*
4.7
0.8
0.8
126
37.3*
36.5
13.5
12.7
127
127
99.2*
51.2*
0.0
26.8
0.8
12.6
0.0
9.4
124
126
75.8*
38.1*
11.3
15.9
5.6
35.7
7.3
10.3
125
46.4*
21.6
20.8
11.2
126
90.5*
4.0
4.0
1.6
125
77.6*
10.4
7.2
4.8
126
126
126
61.9*
65.1*
73.8*
23.0
19.8*
17.5
11.1
11.1
5.6
4.0
4.0
3.2
127
86.6*
11.0
0.8
1.6
127
127
128
67.7*
62.2*
77.3*
14.2
16.5
16.4
5.5
3.1
1.6
12.6
18.1
4.7
128
28.1
42.2*
7.8
21.9
* Modal response. † Refer to the text in the Advisory for the full wording of the questionnaire items.
AION ⫽ anterior ischemic optic neuropathy; CRAO ⫽ central retinal artery occlusion; CVP ⫽ central venous pressure; Hct ⫽ hematocrit;
Hgb ⫽ hemoglobin; ION ⫽ ischemic optic neuropathy; MRI ⫽ magnetic resonance imaging; N ⫽ number of consultants who responded
to each item; PION ⫽ posterior ischemic optic neuropathy.
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Table 3. North American Neuro-Ophthalmology Society Member Survey: Percentage Responses*
Evidence Linkage/Intervention†
1. Preoperative patient evaluation and preparation
Ophthalmic or neuro-ophthalmic evaluation
Vascular risk factors
Preoperative anemia
Prolonged procedures
Substantial blood loss
Prolonged procedures combined with substantial
blood loss
2. Intraoperative blood pressure management
Deliberate hypotension in high-risk patients without
preoperative chronic hypertension
Deliberate hypotension in high-risk patients with
well-controlled preoperative chronic hypertension
3. Management of intraoperative fluids
Intravascular volume should be monitored continually
in high-risk patients
Balance between colloid and crystalloid fluid
resuscitation and replacement
Colloids are preferred over crystalloids
CVP monitoring for high-risk patients
4. Management of anemia
Periodic monitoring of Hgb or Hct for high-risk
patients
5. Vasopressors
Prolonged use of high-dose ␣-adrenergic agonists in
high-risk patients
6. Patient positioning
Avoid direct pressure on the eye
Head position level with or higher than the heart in
high-risk patients
Neutral forward position of head in high-risk patients
Head positioning device not associated with AION or
PION
Horseshoe headrest may increase ocular
compression and perioperative CRAO
Regular assessment and documentation of eyes of
prone-positioned patients
Perioperative facial edema is common in high-risk
patients
7. Surgical procedures
Staging of lengthy procedures
Staging of procedures with substantial blood loss
Staging of lengthy procedures with substantial blood
loss
8. Postoperative management
Assessment of a high-risk patient’s vision when the
patient becomes alert
No proven treatment for perioperative AION or PION
MRI to eliminate causes other than ION and CRAO
In high-risk patients for whom ION is suspected,
adjust Hgb or Hct values upward, increase blood
pressure, and administer arterial oxygenation
No role for antiplatelet agents, steroids, or intraocular
pressure-lowering agents in the treatment of
perioperative ION
N
Agree
Equivocal
Disagree
Opinion
32
30
32
32
32
32
15.6
83.3*
75.0*
81.3*
96.9*
93.8*
40.6
10.0
12.5
15.6
3.1
6.3
43.8*
6.7
12.5
3.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
31
12.9
19.4
41.9*
25.8
31
12.9
12.9
48.4*
25.8
30
80.0*
3.3
0.0
16.7
30
43.3*
13.3
3.3
40.0
29
29
31.0
30.1
17.2
17.2
0.0
0.0
51.7*
51.7*
31
83.9*
9.7
0.0
6.5
31
38.7
12.9
3.2
45.2*
31
31
96.8*
32.3*
3.2
32.3*
0.0
6.5
0.0
29.0
30
31
30.0
32.3*
26.7
22.6
3.3
29.0
40.0*
16.1
31
64.5*
9.7
12.9
12.9
31
83.9*
6.5
3.2
6.5
31
67.7*
6.5
9.7
16.1
32
31
31
50.0*
71.0*
71.0*
21.9
12.9*
9.7
6.3
6.5
6.5
21.9
9.7
12.9
32
81.3*
9.4
3.1
6.3
32
32
32
75.0*
81.3*
90.6*
15.6
12.5
6.3
6.3
3.1
3.1
3.1
3.1
0.0
31
35.5*
35.5*
22.6
6.5
* Modal response. † Refer to the text in the Advisory for the full wording of the questionnaire items.
AION ⫽ anterior ischemic optic neuropathy; CRAO ⫽ central retinal artery occlusion; CVP ⫽ central venous pressure; Hct ⫽ hematocrit;
Hgb ⫽ hemoglobin; ION ⫽ ischemic optic neuropathy; MRI ⫽ magnetic resonance imaging; N ⫽ number of consultants who responded
to each item; PION ⫽ posterior ischemic optic neuropathy.
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Practice Advisory
Table 4. North American Spine Society Member Survey: Percentage Responses*
Evidence Linkage/Intervention†
1. Preoperative patient evaluation and preparation
Ophthalmic or neuro-ophthalmic evaluation
Vascular risk factors
Preoperative anemia
Prolonged procedures
Substantial blood loss
Prolonged procedures combined with substantial
blood loss
2. Intraoperative blood pressure management
Deliberate hypotension in high-risk patients without
preoperative chronic hypertension
Deliberate hypotension in high-risk patients with
well-controlled preoperative chronic hypertension
3. Management of intraoperative fluids
Intravascular volume should be monitored continually
in high-risk patients
Balance between colloid and crystalloid fluid
resuscitation and replacement
Colloids are preferred over crystalloids
CVP monitoring for high-risk patients
4. Management of anemia: Periodic monitoring of Hgb or
Hct for high-risk patients
5. Vasopressors
Prolonged use of high-dose ␣-adrenergic agonists in
high-risk patients
6. Patient positioning
Avoid direct pressure on the eye
Head position level with or higher than the heart in
high-risk patients
Neutral forward position of head in high-risk patients
Head positioning device not associated with AION or
PION
Horseshoe headrest may increase ocular
compression and perioperative CRAO
Regular assessment and documentation of eyes of
prone-positioned patients
Perioperative facial edema is common in high-risk
patients
7. Surgical procedures
Staging of lengthy procedures
Staging of procedures with substantial blood loss
Staging of lengthy procedures with substantial blood
loss
8. Postoperative management
Assessment of a high-risk patient’s vision when the
patient becomes alert
No proven treatment for perioperative AION or PION
MRI to eliminate causes other than ION and CRAO
In high-risk patients for whom ION is suspected,
adjust Hgb or Hct values upward, increase blood
pressure, and administer arterial oxygenation
No role for antiplatelet agents, steroids, or intraocular
pressure-lowering agents in the treatment of
perioperative ION
N
Agree
Equivocal
Disagree
Opinion
20
19
20
20
20
20
0.0
52.6*
45.0*
85.0*
75.0*
90.0*
20.0
21.1
15.0
0.0
10.0
0.0
45.0*
10.5
20.0
10.0
10.0
5.0
35.0
15.8
20.0
5.0
5.0
5.0
20
35.0*
15.0
35.0*
15.0
20
20.0
25.0
40.0*
15.0
20
90.0*
5.0
5.0
0.0
20
30.0
10.0
5.0
55.0*
20
20
20
15.0
55.0*
95.0*
20.0
15.0
5.0
5.0
10.0
0.0
60.0*
20.0
0.0
20
30.0
5.0
0.0
65.0*
20
20
100.0*
30.0*
0.0
30.0*
0.0
10.0
0.0
30.0*
20
20
60.0*
10.0
15.0
10.0
10.0
65.0*
15.0
15.0
19
73.7*
10.5
10.5
5.3
20
95.0*
0.0
0.0
5.0
20
75.0*
15.0
5.0
5.0
20
20
20
60.0*
70.0*
90.0*
20.0
20.0
10.0
10.0
5.0
0.0
10.0
5.0
0.0
20
90.0*
0.0
0.0
10.0
20
20
19
65.0*
55.0*
78.9*
10.0
5.0
5.3
5.0
5.0
0.0
20.0
35.0
15.8
19
0.0
31.6*
5.3
63.2*
* Modal response. † Refer to the text in the Advisory for the full wording of the questionnaire items.
AION ⫽ anterior ischemic optic neuropathy; CRAO ⫽ central retinal artery occlusion; CVP ⫽ central venous pressure; Hct ⫽ hematocrit;
Hgb ⫽ hemoglobin; ION ⫽ ischemic optic neuropathy; MRI ⫽ magnetic resonance imaging; N ⫽ number of consultants who responded
to each item; PION ⫽ posterior ischemic optic neuropathy.
Anesthesiology 2012; 116:274 – 85
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